The utility of internal conversion yields of extrinsic probes of membranes will be assessed using laser flash photolysis. Similarly, the edge excitation red shift for anthroyl probes in model vesicles will be studied to see how useful this effect is for determining intramembrane polarity and viscosity changes. Lastly, polarized energy transfer between external proteins and cell surface membranes containing probes will be studied to infer information about the cell surface membrane as opposed to intracellular membranes. This approach will then be extended to the study of the interaction of 13-cis- and all-trans-retinoic acid with cell surface glycoproteins.